DESCRIPTION: (modified from abstract) The dynamics of enzymatic catalysis reactions will be studied at the molecular level. Raman and IR difference spectroscopies will be used for static measurements and kinetic Raman and IR measurements will be used with submillisecond time resolution, down to 10 ns resolution in some cases, with capabilities to 50 ps when necessary, for dynamic measurements. Emphasis will be on two classes of enzymes: the NAD(P) linked enzymes and the phosphoryl transfer enzymes, both targets for antibacterial and anti-cancer pharmaceuticals. Particular attention will be paid to studying dihydrofolate reductase to understand how the pKa of N5 of the bound dihydrofolate substrate to the E. coli enzyme is raised four units compared to solution. This will be probed by measurements of mutant proteins of different dihydrofolate reductase isoenzymes and of a related protein of the folate family (dihydroneopterin aldolase). Detailed electrostatic calculations will also be used to understand this system. In addition, the c-Harvey ras p21 protein, which contains the essential GTPase core of G-proteins, and the Yersinia enzyme, an example of protein-tyrosine phosphatases, will be studied. The structures of phosphate ground state and the transition state analog complexes of the native protein and a series of mutants will be studied. The kinetics of the binding of ligands to proteins and the motions of flexible loops will be probed by examining ligand binding to lactate dehydrogenase and other proteins, and loop motions will be examined in lactate dehydrogenase, the Yersinia enzyme, and other systems.